The purpose of this contract is to provide genetic monitoring resource to assure the genetic integrity of inbred stock such as F344 rats, B6C3F1 mice and special strains produced for the toxicology and other research and testing programs of the NTP and NlEHS. Up to 20 designated loci will be monitored for each strain or hybrid by electrophoresis of various tissue homogenates and serum proteins. Parental strains of hybrids, hybrids and inbred strains from the foundation, expansion and production colonies will be evaluated for genetic integrity at periodic intervals. Genetic integrity of inbred rodents will be evaluated by skin grafts also. When appropriate, restriction fragment length polymorphisms (RFLPs) and simple sequence length polymorphisms (SSLPs) of DNA by PCR may be evaluated to identify genetic variance. The genetic integrity of the test animals is essential for developing reliable and accurate research data in animal experiments. Continuous monitoring of foundation and production colonies and animals supplied for studies will ensure that data from the NTP and NIEHS animal studies will be collected from genetically homogenous rodents. Genetic homogeneity of test animals will be essential for comparison of studies from different projects and programs for background lesions, lesions between testing facilities, lesions between chemical or physical agents and within the same laboratory overtime.